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Method for brightness enhancement and modes manipulation of a multimode optical fiber

a multi-mode optical fiber and brightness enhancement technology, applied in the field of optical fibers, can solve the problems of reducing beam quality, active fiber lasers capable of maintaining high energy densities along with high beam quality,

Active Publication Date: 2015-05-14
RAFAEL ADVANCED DEFENSE SYSTEMS
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The patent describes a way to control the population of modes without losing power. This is achieved by shifting higher modes into lower modes. The technical effect of this method is that it allows for better control of the mode of oscillation without any energy wastage.

Problems solved by technology

For many years the development of fiber-coupled and active fiber lasers capable of maintaining high energy densities along with high beam quality has been a great challenge.
Due to nonlinear processes and other thermal effects in fibers, parasitic modes are developed; the beam at the output of the fiber is then distorted, resulting in a reduction of beam quality.

Method used

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  • Method for brightness enhancement and modes manipulation of a multimode optical fiber
  • Method for brightness enhancement and modes manipulation of a multimode optical fiber
  • Method for brightness enhancement and modes manipulation of a multimode optical fiber

Examples

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examples

1. Effect of Controlled Strain on Modes Propagation in Optical Fibers

[0071]A theoretical explanation and algorithm for active controlled stress actuation in optical fiber intended to achieve a specific goal (such as brightness enhancement or power in a given area maximization) is now described.

[0072]Consider for example an optical fiber with quadratic refraction index profile of:

n(r)=n(1-n2nr2)1 / 2

[0073]The scalar electric field inside the fiber can be described as follows:

E(x,y,z)=Σm=1NΣn=1NαmnTmn(x,y)eiβmnz

[0074]Where the fiber optical modes are:

Tmn(x,y)=1ωxωyπ(m-1)(n-1)2m+n-3Hm(2xωx)Hn(2yωy)-x2ωx2-y2ωy2andwhereβmn=k[1-2kn2n(m+n+1)]1 / 2

[0075]The model for fiber distortions is derived herein. Assume the following modal distribution at z=0 position within the fiber:

αmn=ζ(m2+n2)v

[0076]Where ζ is random number ranging [−1, 1] with flat distribution and v is a constant defining the modal constitution of the beam.

[0077]The beam segment is distorted by phase masks located at predefined po...

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Abstract

The invention relates to adaptive optics techniques applied to alter the modal structure of light propagating in an optical fiber. In particular the invention relates to altering the modal structure in a multimode beam propagating in a multimode fiber by lowering the number of higher modes. The method comprises combining a wavefront sensor and / or a power sensor with a phase control actuator and actuator control algorithms, to alter the phase structure of the beam thereby to eliminate higher modes. The corrected beam can be then effectively coupled into a smaller diameter fiber with minimum loss of energy and concentrated to smaller spot sizes limited by diffraction.

Description

FIELD OF THE INVENTION[0001]The present invention relates to optical fibers. More particularly the invention relates to a method for altering modal structure of light propagating in an optical fiber.BACKGROUND OF THE INVENTION[0002]Optical fibers are of great importance in many fields of science and technology. There are various parameters of optical fibers affecting their properties; one of the most important is the number of modes capable of non-attenuated propagation. Fibers carrying only a single transverse mode are called single mode (SM) fibers. Fibers capable of propagating more than one mode are called multimode fibers (MM). Different fiber modes have different propagation properties, e.g. group velocity, spatial intensity and phase profiles. Modal group velocity dependence in MM fibers affects the fiber's ability to transmit data along longer distances. Intensity and phase dependence affect the beam quality factor, i.e. the M2 parameter, of the beam exiting the fiber. This ...

Claims

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Application Information

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IPC IPC(8): G02F1/035G02F1/01H01S3/067
CPCG02F1/035G02F1/0115H01S3/067G02B6/14
Inventor REGELMAN, DAN VADIMSEGEV, YEHONATANYOSUB, SHAY
Owner RAFAEL ADVANCED DEFENSE SYSTEMS